Law enforcement authorities on Monday said they halted two loosely organized gun-smuggling operations and confiscated more than 250 firearms — which the New York Police Department claims is the largest such seizure in the agency’s history.

The operation involved a single undercover officer who purchased 254 guns in 45 separate transactions, authorities said. The weapons were transported from two southern states through means including low-cost buses to Manhattan’s Chinatown, Police Commissioner Raymond Kelly and Mayor Michael Bloomberg said.

The seized firearms vary from .22 caliber pistols to semi-automatic rifles. “Among the guns sold were a fully automatic Cobray 9 millimeter machine gun with a 30-round high-capacity magazine” and three Intertec 9 pistols with flash suppressors and magazines that hold 30 or more rounds, according to a news release.

In all, police arrested 19 people in New York, North Carolina and South Carolina, including Walter Walker and Earl Campbell, who allegedly smuggled the guns to New York, authorities said.

The 19 were charged with crimes including conspiracy, selling firearms and weapons possession in a 552-count indictment filed by the Office of the Special Narcotics Prosecutor. The indictment centers on 208 guns that were sold for nearly $160,000.

Law enforcement officials obtained court-authorized wiretaps as part of the investigation. On one of the taps, Mr. Campbell was allegedly recorded saying it’s difficult to sell the weapons in the city because of the NYPD’s stop-and-frisk tactic, officials said.

“Yeah I’m in Charlotte now. I can’t leave until you come, cause I can’t take them [guns] to my house, to my side of town cause I’m in Brownsville. So we got like, whatchamacallit, stop and frisk,” Mr. Campbell allegedly said, according to the indictment.

Authorities have said that lax gun laws in other states makes New York, which has some of the strictest gun laws in the country, a target for illegal firearms. The guns can fetch three times as much money on the black market in New York.

Authorities would not go into details about how the undercover officer was introduced to Mr. Walker.

The investigation, which began in August 2012, grew out of a undercover narcotics operation in Brooklyn, Police Commissioner Raymond Kelly said.

Watch a video of excerpts from Mayor Bloomberg’s announcement of the seizure here: